STIHL FS 72 Service Manual

The STIHL FS 72 is a professional-grade trimmer/brushcutter designed for demanding clearing and trimming tasks. This manual provides detailed service, maintenance, and repair information for the FS 72 powerhead, including its 2-stroke engine, fuel system, ignition system, cutting attachments, and safety features. Below are key sections covering specifications, safety, maintenance procedures, troubleshooting, and parts information.

1. Features at a Glance 2. Safety Information 3. Specifications 4. Maintenance Schedule 5. Fuel System Service 6. Ignition System Service 7. Engine Service 8. Cutting Attachment Service 9. Troubleshooting 10. Parts Diagrams 11. Warranty & Support

Features at a Glance

Key components: 2-stroke engine with electronic ignition, anti-vibration system, translucent fuel tank, quick-stop inertia chain brake (if equipped with cutting blade), side-mounted carburetor, and compatibility with various STIHL trimmer heads and blades.

Feature	Description
Engine Type	STIHL 2-MIX 2-stroke, single cylinder
Displacement	Approx. 31.8 cc (1.94 cu. in.)
Power Output	Approx. 1.3 kW (1.8 hp)
Fuel System	Diaphragm carburetor with manual choke
Ignition System	Electronic, capacitor discharge (CDI)
Starting System	Rewind starter with decompression valve
Anti-Vibration	Integrated anti-vibration system in handles and shaft
Fuel Tank Capacity	Approx. 0.55 liters (18.6 fl. oz.)
Recommended Fuel	Unleaded gasoline min. 89 octane mixed with STIHL 2-stroke oil (50:1)
Cutting Attachment	Accepts STIHL PolyCut heads, circular saw blades, and brush knives

Safety Information

Always wear appropriate Personal Protective Equipment (PPE): safety glasses, hearing protection, gloves, sturdy boots, and long pants. Ensure the unit is on a stable surface before starting. Keep bystanders and pets at a safe distance.

Before Starting: Check for loose fasteners, damaged parts, and ensure cutting attachment is properly installed and secure.
During Operation: Maintain firm footing and grip. Do not operate above shoulder height. Be aware of kickback zone with cutting blades.
Fuel Safety: Refuel in a well-ventilated area with engine stopped and cool. Wipe up spills immediately. Store fuel in approved containers.
Maintenance Safety: Disconnect spark plug boot before performing any service except carburetor adjustment.

WARNING! Failure to follow safety instructions can result in serious injury or death. Read and understand the operator's manual before use.

Specifications

Model: STIHL FS 72
Engine: Air-cooled, 2-stroke single-cylinder with STIHL 2-MIX technology
Displacement: 31.8 cm³
Powerhead Weight (dry): Approx. 5.9 kg (13.0 lbs)
Idle Speed: 2,800 rpm
Maximum Power Speed: Approx. 9,500 rpm
Spark Plug: Bosch WSR 6 F or equivalent, gap 0.5 mm (0.020 in)
Carburetor: Zama C1Q-S series (adjustable H, L, LA screws)
Fuel/Oil Ratio: 50:1 (STIHL 2-Stroke Oil or equivalent ISO-L-EGD quality)
Sound Pressure Level: Approx. 96 dB(A) (measured per standard)
Vibration Level: Front handle: < 2.5 m/s²; Rear handle: < 5.0 m/s²

Maintenance Schedule

Regular maintenance is crucial for performance, longevity, and safety. Follow this schedule based on hours of operation or as needed.

Item	Before Each Use	Every 25 Hours	Every 50 Hours	Every 100 Hours
Check for loose fasteners	✓
Clean air filter		✓
Replace air filter			✓ (or if damaged)
Check spark plug		✓
Replace spark plug				✓
Clean spark arrestor screen (if equipped)			✓
Check fuel filter			✓
Replace fuel filter				✓
Clean cooling fins			✓
Grease drive shaft (if applicable)				✓

Fuel System Service

Includes carburetor adjustment, fuel line replacement, and fuel filter service.

Carburetor Adjustment (Idle, Low (L), High (H)): Engine must be at operating temperature. Use a tachometer.
- Start engine and warm up for several minutes.
- Set idle speed screw (LA or T) to achieve 2800 rpm.
- Adjust low-speed screw (L) for smoothest acceleration from idle.
- Adjust high-speed screw (H) for maximum rpm (not to exceed no-load max speed spec).
- Re-check idle speed and adjust if necessary.
Fuel Line Replacement: Disconnect spark plug boot. Drain fuel tank. Remove old lines from tank grommet and carburetor. Install new lines, ensuring they reach the bottom of the tank.
Fuel Filter Replacement: Pull filter from fuel line inside tank using a wire hook. Attach new filter to line and insert into tank.

CAUTION! Use only STIHL or approved replacement parts. Improper carburetor adjustment can cause engine damage.

Ignition System Service

Testing spark plug, ignition module (coil), and stop switch.

Spark Plug: Remove, inspect electrode for wear and deposits. Clean or replace. Set gap to 0.5 mm (0.020 in).
Ignition Module Test: Use an ignition tester. Connect tester between spark plug boot and a good ground on cylinder. Pull starter. A strong, consistent spark indicates good module. No spark requires module replacement.
Stop Switch Test: With spark plug removed and boot grounded, disconnect the stop switch wire from the module. Pull starter. If spark appears, the stop switch or wire is faulty.

Note: The ignition module is non-adjustable. If faulty, replace entire unit.

Engine Service

Cylinder and piston inspection, muffler service, and decompression valve.

Compression Check: Use compression gauge. A reading below 100 psi (6.9 bar) indicates worn piston rings, cylinder, or leaking seals.
Cylinder/Piston Inspection: Remove muffler and look through exhaust port. Scratches on piston or cylinder wall indicate damage. Remove cylinder for detailed inspection.
Muffler/Spark Arrestor: Remove muffler cover. Clean carbon deposits from spark arrestor screen with a wire brush. Do not remove screen.
Decompression Valve: Located on cylinder head. Ensure it moves freely and seals. Replace if leaking (hissing sound when pulling starter).

WARNING! Major engine disassembly requires special tools and expertise. Consult an authorized STIHL service dealer for complex repairs.

Cutting Attachment Service

Trimmer head maintenance and blade installation.

PolyCut Head Line Replacement: Press in tabs on bump knob, remove knob. Remove spool, wind new line onto spool following directional arrows. Reassemble, pulling ends of line through eyelets.
Blade Installation: Ensure engine is off and spark plug disconnected. Use correct blade bolt, washer, and nut. Tighten bolt securely with appropriate wrench. Ensure blade guard is properly installed.
Drive Shaft/Gearhead: Check for smooth rotation. Grease gearhead per maintenance schedule using STIHL special grease.

CAUTION! Always use STIHL-approved cutting attachments. Improperly installed blades can come loose and cause severe injury.

Troubleshooting

Symptom	Possible Cause	Corrective Action
Engine will not start	No fuel, flooded, no spark, clogged air filter	Check fuel, dry plug, test spark, clean/replace air filter.
Engine starts but dies	Clogged fuel filter, dirty carburetor, faulty ignition	Replace fuel filter, clean carburetor, check ignition module.
Loss of power	Clogged air filter, spark arrestor, carburetor adjustment	Clean air filter & spark arrestor, adjust carburetor.
Excessive vibration	Bent drive shaft, unbalanced blade, loose fasteners	Inspect shaft and blade, tighten all fasteners.
Cutting attachment does not turn	Sheared clutch spring, broken drive shaft	Inspect clutch and shaft, replace damaged parts.
Engine overheats	Dirty cooling fins, lean carburetor setting, low oil mix	Clean fins, adjust carburetor (richen), use correct fuel mix.

Reset: For electronic issues, disconnect spark plug boot for 1 minute to reset ignition module.

Parts Diagrams

Refer to official STIHL parts catalog for exploded-view diagrams and part numbers for the FS 72 powerhead, cutting attachments, and accessories. Common replacement parts include:

Air Filter (Part # XXXX-XXX-XXXX)
Fuel Filter (Part # XXXX-XXX-XXXX)
Spark Plug (Bosch WSR 6F)
Carburetor Repair Kit (Part # XXXX-XXX-XXXX)
Ignition Module (Part # XXXX-XXX-XXXX)
Starter Rope & Spring (Part # XXXX-XXX-XXXX)

Note: Always use genuine STIHL parts to ensure performance, safety, and warranty compliance.

Warranty & Support

STIHL FS 72 is backed by a limited warranty from date of purchase. Warranty covers defects in materials and workmanship under normal use. It does not cover damage from misuse, lack of maintenance, or use of non-STIHL parts/fuel.

For technical support, service, or to locate a dealer:

Visit: www.stihlusa.com
Customer Service: 1-800-467-8445

This manual is a supplement to the original operator's manual. Always refer to the latest STIHL documentation for the most current information.